Synergistic lubrication performance by incommensurately stacked ZnO-decorated reduced graphene oxide/MoS₂...

Incommensurate stacking between two different types of two-dimensional layered materials furnished the weak interfacial interaction due to the mismatch of their lattice structure, which can be harnessed for development of new generation lubricant additives. Herein, a facile approach is presented to synthesize the ZnO-decorated reduced graphene oxide/MoS₂ (Gr-MS-Zn) nanosheets. The Fourier transform infrared, X-ray photoelectron spectroscopic, Raman, and transmission electron microscopic analyses confirmed the preparation of Gr-MS-Zn heterostructure. The MoS₂ nanosheets having 3-7 molecular lamellae are thoroughly distributed over the graphene skeleton via weak interfacial interaction. The curved and bent structure of MoS₂ nanosheets grown over the graphene lamellae subsidized the cohesive interaction and furnished the stable dispersion of Gr-MS-Zn in the fully formulated engine oil. The minute dose of Gr-MS-Zn as a nano-additive to engine oil significantly enhanced the tribological performance between the steel-steel tribopair by decreasing the friction (37%) and the wear volume (87%). The microscopic and spectroscopic analyses revealed the formation of a Gr-MS-Zn-based surface protective tribo thin film of low shear strength. The enhanced tribo performance is collectively attributed to (a) uninterrupted supply of ultrathin Gr-MS-Zn nanosheets to tribo-interfaces, (b) stable dispersion of Gr-MS-Zn, and (c) the significantly low shear strength, arising from weak interfacial interaction between the incommensurately stacked graphene and MoS₂ nanosheets.